The present invention relates generally to a shaft coupling and more particularly to a shaft coupling within an overrunning clutch apparatus which transmits rotary power in only one direction.
The problem of how to couple one shaft to another for transmitting a torque force is a longstanding one. This has particularly been true in the farming community because the power take-off of an agricultural tractor frequently needs to be connected and disconnected to utilize one implement and then another. This problem has been solved in the past in one degree or another, and one of the most commercially successful of these solutions is a connection of the type disclosed in U.S. Pat. No. 3,448,278, which was patented in 1948.
In U.S. Pat. No. 2,448,278, a pin is spring biased to one position within a coupling housing such that it will contact and hold one spline of a power take-off to thereby hold the coupling together. In another position of the pin, it is moved so that it does not block or contact any of the splines and thereby allows the housing to be removed from the power take-off shaft. Since 1948 when the above mentioned patented coupler was developed, the horsepower rating of typical agricultural tractors has continued to increase. Because of the very high torque which can be developed from the power take-offs of modern-day agricultural tractors, it is desirable that the coupling be held at more than one point and on more than one spline of the power take-off shaft. A French Pat. No. 1,102,886 patented in France in 1955, discloses a design for locking on all of the splines of a power take-off shaft, but this design has not become a commercial success, at least not in this country, presumably because of its somewhat complicated structure utilized to position and bias the locking splines.
While it has long been the standard procedure to directly couple a farm implement to a farm tractor through a solid coupling as discussed above, it has been found that there are many instances when it is desirable to interpose what is commonly called an overrunning clutch in the transmission line between the power take-off of the tractor and the implement being utilized. This is particularly true for machines which produce a high degree of inertial forces such as the rotary mowers or choppers which are in common usage. When the blades of such machines are rotated at high speeds, they have a considerable amount of inertia or momentum which causes them to continue rotation even when the tractor is stopped. Such continuation of the rotation of the cutting blades will then often be transmitted by the drive shaft to the power take-off of the tractor, causing the tractor to move ahead along the ground beyond the point where it was intended to be stopped. This may be true even when the clutch pedal of the tractor is depressed. This is particularly a problem for tractors which do not have the feature commonly called live power. Accordingly, power take-off connections of the type commonly referred to as an overrunning clutch have been developed. An example of such a connection is disclosed in U.S. Pat. No. 3,233,471.
U.S. Pat. No. 3,233,471 discloses an overrunning clutch having a pin which is received through an inner member and through the power take-off shaft of a tractor in order to maintain a positive connection between these two members. It is very important that a positive connection be formed.
While the coupling of U.S. Pat. No. 3,233,471 is very dependable, it is more time consuming to connect than the standard disconnect couplings such as disclosed in U.S. Pat. No. 2,448,278, which does not have the overrunning clutch connection as a part thereof. Accordingly, there is a genuine need to have an overrunning clutch coupler which is of a quickly detachable variety. Additionally, there are some power take-off shafts which do not have a hole passing therethrough, and consequently, the power take-off connection disclosed in U.S. Pat. No. 3,233,471 would not be suitable for use under such conditions.
The power take-off shafts of tractors normally have longitudinal splines and grooves around the periphery thereof. The standard number of splines on older tractors is six, while the standard number of splines on newer tractors is usually twenty-one. Since it is clear that if the same size of shaft has a larger number of splines thereon, that these splines will be smaller and each spline will have less strength. This is particularly important when considering the use of the coupling as disclosed in U.S. Pat. No. 2,448,278, since this type of coupling engages only one or possibly two of the splines, the smaller splines could possibly be subject to unbearable forces in use with the high horsepower tractors of today. Accordingly, it is readily apparent why it is desirable to be able to hold a power take-off shaft on each of its splines, rather than on only one or two.